1. Field of the Invention
The present invention relates generally to the field of air conditioning systems. In particular, the present invention relates to air conditioning systems employing a refrigerant circuit to decrease a temperature of an inverter.
2. Description of Related Art
Known air conditioning systems may control the rotational speed of an operating compressor by controlling the rotational speed of an electric motor driving the compressor. Specifically, known air conditioning systems may control the rotational speed of the compressor via an inverter. Moreover, in order to prevent an air conditioning load from increasing beyond a predetermined level, the rotational speed of the electric motor may be decreased when the amount of electrical current flowing to the electric motor exceeds a predetermined amount of electrical current. As such, the amount of electrical current flowing to the electric motor generally may be maintained below the predetermined amount of electrical current, which may reduce damage to the inverter caused by excessive electrical current. Nevertheless, in such air conditioning systems, when the amount of electrical current flowing to the electric motor is greater than the predetermined amount of electrical current, the rotational speed of the motor will be decreased, which causes a cooling capacity of the refrigerant circuit to decrease.
Japanese Patent (Unexamined) Publication No. H10-115448 describes an air conditioning system that substantially maintains the cooling capacity of the refrigerant circuit, while also maintaining the amount of electrical current flowing to the electric motor below the predetermined amount of electrical current. In this air conditioning system, the amount of electrical current flowing to the electric motor, and the rotational speed of the electric motor, are correlated to a torque of the compressor, i.e., the load torque. When the amount of electrical current flowing to the electrical motor is a constant value, the torque of the compressor decreases and the rotational speed of the electric motor increases. Consequently, even when the amount of electrical current flowing to the electric motor decreases, the rotational speed of the electric motor may be maintained by decreasing the torque of the compressor.
Specifically, the foregoing air conditioning system may decrease the volume of air passing through an evaporator. Decreasing the volume of air passing through the evaporator may decrease the amount of electrical current flowing through the electric motor and also may increase the rotational speed of the electric motor. Moreover, increasing the rotational speed of the motor also decreases the torque of the compressor and maintains a substantially constant air conditioning system cooling capacity.
Nevertheless, in the foregoing air conditioning system, although the amount of electrical current flowing to the electric motor is maintained below the predetermined amount of electrical current, the amount of heat generated by the inverter may be greater than an amount of heat which is absorbed by the refrigeration circuit. Consequently, although the amount of electrical current flowing to the electric motor is maintained below the predetermined amount of electrical current, the inverter may be damaged.
Therefore, a need has arisen for air conditioning systems and methods of employing such air conditioning systems that overcome these and other shortcomings of the related art. A technical advantage of the present invention is that the rotational speed of a compressor may be reduced when the temperature of the inverter becomes greater than a first predetermined temperature. Moreover, a rotation of the compressor may be stopped when the temperature of the inverter becomes greater than a second predetermined temperature which is greater than the first predetermined temperature. Reducing the rotational speed of the compressor, or stopping the rotation of the compressor, or both, may reduce or eliminate damage to the inverter.
According to an embodiment of the present invention, an air conditioning system is described. The air conditioning system comprises a refrigerant circuit. The refrigerant circuit comprises a compressor for receiving a refrigerant gas and for compressing the refrigerant gas, and a condenser for condensing a portion of the compressed refrigerant gas into a liquid refrigerant. The refrigerant circuit also comprises an expansion valve for reducing a pressure of the condensed liquid refrigerant, and an evaporator for evaporating the condensed liquid refrigerant. Moreover, the compressor is driven by an electric motor which controls the rotational speed of the compressor via an inverter, and a temperature of the inverter is decreased by the refrigerant circuit. The system also comprises means for determining whether a temperature of the inverter is greater than a first predetermined temperature, e.g., an electric circuit, and means for controlling the rotational speed of the compressor, e.g., an electrical circuit. Specifically, when the temperature of the inverter is greater than the first predetermined temperature, the means for controlling the rotational speed of the compressor decreases the rotational speed of the compressor. In another embodiment, the inverter is formed integrally with the compressor.
According to another embodiment of the present invention, a method of employing an air conditioning system is described. The air conditioning system comprises a compressor for receiving a refrigerant gas and for compressing the refrigerant gas, and a condenser for condensing at least a portion of the compressed refrigerant gas into a liquid refrigerant. The air conditioning system also comprises an expansion valve for reducing a pressure of the condensed liquid refrigerant, and an evaporator for evaporating the condensed liquid refrigerant. Moreover, the compressor is driven by an electric motor, and the electric motor controls a rotational speed of the compressor by an inverter. The method comprises the steps of determining whether a temperature of the inverter is greater than a first predetermined temperature, and decreasing a rotational speed of the compressor when the temperature of the inverter is greater than the first predetermined temperature.
Other objects, features, and advantages of the present invention will be apparent to persons of ordinary skill in the art in view of the following detailed description of the invention and the accompanying drawings.